I saw someone with a Nexus 5 yesterday. He carries a huge external battery pack (at least twice the size of the phone) and re-charges 2-3 times daily! He would love 16 hours battery life.
I agree with those who place battery life over thinness and weight. Once a device is thin and light enough (e.g. iPhone 4), I'd rather have one that lets me do more in a day.
I'd rather wait and see what the real product is like before I worry about battery life based on rumoured specs. If Apple can really manage to improve battery life without significantly increase the size of the battery it's better because I dont have to charge it for too long.